In three-dimensional integrated circuits, interposers are used for bonding devices. Interposers are often passive interposers, wherein there are no active devices such as transistors formed in the interposers. Through-Silicon Vias (TSVs) are used to make electrical connections from one side of an interposer to the opposite side. Further, there may be metal routing layers on one side or both sides of an interposer, wherein the metal routing layers are used to electrically connect solder bumps on the surface of the interposer to the TSVs, and to electrically interconnect the solder bumps.
Conventionally, before the interposers are bonded to other package components, the connections in the interposers are often open connections. It is difficult to test the interposers having the open connections efficiently. The conventional boundary scan testing cannot be used if the interposers are to be tested before dies are bonded thereon.